What is A GMT Watch – Simply Explained

There are a lot of watches which have a bezel, maybe even several bezels. The bezels on watches (including the movement) is essentially what changes the purpose of a watch. The essential function of a watch is that it can tell time. The bezel and the modification made to the movement is what can add further features to the watch, such as a GMT function.

GMT is a function which gives a watch an additional time zone. The timepiece has a 24 hour hand that indicates a second timezone on the 24-hour bezel, typically placed as an external bezel. A clockwise rotation of the bezel will subtract from the GMT, while counter-clockwise will add to the GMT.

The history of a GMT is more or less what you would expect. However, what a GMT watch can be used for might surprise you. Furthermore, there is a misconception between GMT and dual time watches.

What is a GMT Watch?

A GMT watch is a spectacular timepiece. While the function it offers is nothing complicated with today’s technology and the extra 24-hour hand can make it look more cluttered compared to a regular watch. A GMT lets you see the time in 2 different time zones at a glance. No calculation of time zone of +3 GMT to -5 GMT etc. is needed.

In simple words, a timepiece with a GMT function has a 24-hour hand, which is used to tell the time in another time zone from a 24-hour bezel. The bezel can be rotated bidirectionally to go forward or backward in GMT.

In addition to the hour, minute, and second hand on a typical watch, a GMT features an additional hand which is rotating once every 24-hours. From a technical point of view, it is attached to the 12-hour hand, but on a larger cog, in such a way that it will rotate exactly half the speed of a 12-hour hand.

There is a distinction between a dual-time watch and a GMT watch. A common misconception is that a GMT is everything that shows 2 different time zones. However, the watch is required to have a 24-hour bezel giving the GMT function. A GMT watch with a 24-hour bezel is what is known as a true GMT.

A GMT watch typically has 2 colors on the bezel. The colors indicate the daytime and nighttime. The colors used generally are red and blue. However, there are many color variations. The colors separate at 6 PM and 6 AM (or 18:00 and 06:00). From 06:00 to 18:00, the bezel is red, and from 18:00 to 06:00, the bezel is blue. The bezel will, therefore, also show the light source in the time zone. Such a feature is beneficial for people unfamiliar with the 24-hour time system (such as Americans). It is helpful for pilots that fly a lot, constantly turning the bezel to fit the next destination’s time zone.

A GMT watch can be used for 3 different purposes. The most commonly used is keeping track of 2 time zones, the local and the second time zone. Then a more uncommon way of using the GMT is keeping track of 3 different time zones. While it is not fairly more advanced than tracking 2 time zones, it needs some getting used to. Lastly, is the function of using the GMT as a compass if you are in the northern hemisphere.

What is GMT and What Does it Mean?

GMT stands for Greenwich Mean Time and originates from the Royal Observatory in Greenwich, London. London has the GMT +0, which is the “center” of the GMT scale. At the furthest forward time zone is +14 in Kiribati, located in the Pacific Ocean. The furthest behind is some Islands owned by the U.S. in the -12 GMT zone.

GMT is a standard that is used to differentiate between time zones. The GMT was initially invented to help to aid naval navigation. Every 15 degrees longitude represents one hour’s difference in time. Therefore, you will also find that 15*24=360, or a circle like the earth (sorry flat-earthers).

The History Behind GMT Watches

The history of GMT watches starts with Rolex. Rolex and Pan Am airlines came together to find a solution for timekeeping for pilots. The story goes that the crew onboard the planes couldn’t keep track of time, and while they were expected to jump between timezones, it was problematic for the pilots.

Rolex GMT-Master
Rolex GMT-Master

Pan Am airlines and Rolex developed a watch that pilots could use to track the clock at both departure city and destination, that watch is known as the Rolex GMT-Master.

The watch launched in 1955, with the iconic red and blue bezel that has come to be known as the Rolex Pepsi. Since then, Rolex has released new models of the Rolex GMT variant, amongst those are the Rolex GMT-Master II, with bezels of black and bronze (nicknamed Rootbeer), black and blue (nicknamed Batman), and black and red (nicknamed Coke). The visual of the watch has evolved in terms of the technology used, e.g., the bezel is made of ceramic on newer models compared to the original GMT-master with an aluminum bezel. However, the functionally of the watch has stayed the same ever since.

The irony of the Rolex GMT history is that Pan Am airlines went bankrupt in 1991, while the Rolex GMT variants all have gone up in value. The vintage Rolex GMT-Master reference 1675 went from a €5,000, and now they are easily somewhere between $10,000 to $15.000.

Difference Between Dual Time and GMT

Sinn 856 UTC Dual Time Watch
Sinn 856 UTC Dual Time Watch

There is a common misconception between dual time watches and GMT watches. They are not the same and serves two different purposes. While many dual time watches being similar to GMT watches, they are not the same. A GMT watch tells the time locally and at a tracking GMT zone from a 24-hour adjustable bezel. A dual time shows time in two different time zones. The main difference being a dual time doesn’t have a 24-hour GMT adjustable bezel.

The GMT watch has a 12-hour hand, minute hand, and second hand. Also, it has a 24-hour hand, which is read from a 24-hour bidirectional bezel. The best example is to look at a Rolex GMT-Master. Those where the first, and hence best represent a true GMT.

In contrast, a dual time watch can have a main dial and a sub-dial. They can both be 12-hour scale. However, the watch can also feature a 12-hour dial with a 24-hour scale within. A good example of dual time watches are the Sinn 856 UTC and Patek Philippe Nautilus Travel Time Chronograph reference 5990/1A. Both watches are dual times, allowing the wearer to see the time of two time zones at a glance. However, none of them are a true GMT as they have no adjustable bezel to go forward or backward in GMT.

How to Use a GMT Watch

A GMT watch is a highly functional watch. With the possibility to see the time in a different time zone at a glace can be essential for the global businessman, the traveler, people living abroad, or the pilot. It is a stunning timepiece in terms of functionality for the right user.

There is some debate in regards to how the watch should be set. A purist would claim that the GMT should be GMT +0. Then the bezel should be turned according to the time zone you wanted to track. However, you can use the GMT however you like, and setting the GMT to +0 is not required to read the time.

A GMT watch can be used in one of three ways. To track two or three time zones or work as a compass. The tracking of two time zones is the common use of the GMT watch. It is for the pilot knowing the local time at take-off and tracking time at the destination, the stock trader trading local shares and waiting for the foreign markets to open, “that one” from the family living abroad wanting to keep track of when it is responsible for calling home, etc.

Tracking 3 time zones is for the serious time traveler, one with family or loved once in multiple time zones, a business owner with businesses or employees in numerous countries or time zones. While tracking 3 time zones at once can be a bit confusing, it is easy to adjust to, as long as you know the GMT difference between the zones.

Using the watch as a compass can be a beneficial tool if you are at an open sea, or driving in unknown areas.

Enough talk, let’s get to how you actually set the time!

How to Set the GMT Watch for 2 Time Zones

Setting the GMT watch is quite easy, actually. Setting the time is essentially a three-step process, but I will try to dive as deep as possible to help you get each step right.

Set it as the purists want (GMT +0, or London time):

  • Step 1: Wind the watch if it has stopped.
  • Step 2: Set the 24-hour hand to the GMT +0 (same time zone as London).
  • Step 3: Set the minute hand, so it matches the GMT. E.g., the GMT is 22:15, the GMT hand (the 24-hour hand) should be placed at 22 from step 2. Now set the minute hand to 3 (or 15 minutes).
  • Step 4: Set the 12-hour hand to the local time. The hour hand is typically jumping one hour at a time. This means that if the local time is 9:40, it can look like you have set it to 10:40, because the hour hand has progressed so long into the hour. Just be aware.
  • Step 5: Figure out which GMT zone to track. E.g., if you are in Miami, USA, the GMT is -6. You can see all the time zones here.
  • Step 6: Rotate the bezel to the GMT wanted. Turning the bezel clockwise will lose time (i.e., minus GMT), and counter-clockwise will gain time (i.e., positive GMT). Using the Miami example, turn the bezel 6 clicks clockwise.

Using the “purist” method, the bezel will be skewed to one side or the other. If you are slightly OCD, that will annoy the crap out of you.

Set it, so the zero-mark from the 24-hour bezel aligns with the 12-hour mark, non-purist style:

  • Step 1: Wind the watch if it has stopped.
  • Step 2: Set the GMT hand to the GMT zone you want to track. E.g., the GMT is 22:15, the GMT hands should point to the 22 mark on the GMT bezel, and the minute hand should be pointing at 3 (or 15 minutes). All the hands will move now, but don’t worry about it for now. You can see the GMT zones here.
  • Step 3: Set the hour hand to the local time.

How to set the GMT watch for 3 time zones

The GMT bezel must be aligned to the 12-hour mark on the dial to track 3 time zones. You need to know the 24-hour time zone on the 12-hour dial if you wish to glance at the dial to see the time for the second time zone. This will need some getting used to, but it is possible.

  • Step 1: Wind the watch if it has stopped.
  • Step 2: Set the GMT hand to the GMT zone you want to track. E.g., the GMT+5 is 22:15, the GMT hands should point to the 22 mark on the GMT bezel, and the minute hand should be pointing at 3 (or 15 minutes). All the hands will move now, but don’t worry about it for now. You can see the GMT zones here.
  • Step 3: Set the hour hand to the local time.
  • Step 4: You can now rotate the bezel to track a third-time zone. It requires you to know the difference between the GMT zone and the third time zone. E.g., the GMT is set to track GMT+2, and the third time zone should be GMT +5. You will rotate the bezel 3 clicks counter-clockwise to gain the difference (5-2=3). Turning the bezel clockwise will lose time (i.e., minus GMT), and counter-clockwise will gain time (i.e., positive GMT).

How to use the GMT as a compass

While this is a feature not used by most, it is nonetheless very cool. If you are the owner of a GMT and you occasional sail or drive in completely unknown areas, this could help you find the way if you know which direction to go.

Northern Hemisphere
Image showing the northern hemisphere

However, for the compass feature to work, you must be in the northern hemisphere and have both the hour hand and the GMT set to local time. The GMT bezel’s 24-hour mark must be aligned with the 12-hour mark on the dial.

  • Step 1: Wind the watch if it has stopped.
  • Step 2: Set the GMT hand to local time on the 24-hour bezel.
  • Step 3: Set the minute hand to local time.
  • Step 4: Set the hour to local time.
  • Step 5: Place the watch on any flat surface. It should be leveled horizontally, e.g., a table, dashboard of a car, palm of your hand, etc.
  • Step 6: Point the hour hand towards the sun. The GMT hand will now point north. Science…

What is the Purpose of Two Colors on a GMT Bezel?

The purpose of the colors on a GMT bezel is to illustrate whether it is day time or night time in the tracking time zone. On the “Pepsi” bezel, the blue area represents night time and goes from 18:00 to 06:00. The red zone illustrates the daytime and goes from 06:00 to 18:00.

Not only is the time easily adjustable with the 24-hour GMT bezel, but also do you get whether it is day time or night time. Such function can be helpful when just glancing at the watch, or for people not familiar with the military time. Americans using AM and PM to tell whether it is AM = before noon or PM = afternoon will have a better experience using a double-colored bezel than a single-colored bezel.

The military time scale is the 24-hour scale used in Europe. In counties where the military time is not standard scale, it is typically used in military, hospital, tourism, etc.

Jonas Henriksen

AllInWatches is founded by Jonas, who has a great interest in mechanical watches. All aspects of manual and automatic (mechanical) watches is a big interest and have been a passion since 2015, where the first automatic watch was purchased. Seeing the transparent case back and discovering the heritage of watchmaking piqued an interest in horology.

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